[UX - Add project to sln] eliminate longest common prefix of all fsproj in the list

[smoothdeveloper]

I wanted to add a .fsproj in my .sln but the path doesn't show me the relevant part, so I can't pick the particular project:

I think the right and no risk thing would be to replace the longest subprefix shared by all projects with something showing relative path, or maybe, to make all the items relative to the sln (which must be identical to what will eventually get written in the file.